An optical communication network for exchanging information at low cost, like a Fiber to the Home (FTTH) or a computer network using light, has a single optical fiber distribution network which connects between a center office or a host and, an individual subscriber or terminal through a single-strand optical fiber, which is one way of reducing an installation cost of optical fibers. Wavelength division multiplexing (WDM) in which a wavelength of signal light is divided prior to use is employed to simultaneously transceive information through the single optical fiber distribution network.
An optical module has been manufactured such that a laser diode (to be abbreviated as LC hereinafter) module and a photodiode (to be abbreviated as PD hereinafter) module are separately fabricated and incorporated into the optical module. In recent years, however, the FTTH or the computer optical network having an advantageous feature of cost effectiveness has gained popularity. Accordingly, there has been rapidly increasing demand for a bi-directional optical module capable of simultaneously transceiving an optical signal through a single-strand optical fiber. Such a conventional bi-directional optical module, as shown in FIG. 1, has been assembled such that a top open (TO) type LD module 1 and a TO type PD module 2 are simply combined with each other around an optical filter 3.
In the above-described bi-directional optical module, that is, a simply assembled package of TO type LD and PD modules, the TO type LD module and the TO type PD module are separately used, so that the module package becomes bulky, making it difficult to achieve miniaturization. Thus, it is quite difficult for the bi-directional optical module to satisfy the Small Form Factor Pluggable Transceiver Multi-Source Agreement (SMF MSA) which has been recently internationally standard. In addition, a distance between the LD and PD modules increases, e.g., 10 mm or more, optical axes of the LD and PD modules may often be misaligned due to cumulative errors, including a precision error metal blocks supporting the LD and PD modules, errors in positions in a lens, an optical filter, and the like, much time is required for optical alignment, and inferiority in the reception sensitivity may become relatively severe.
Meanwhile, since the bi-directional optical module is configured such that the LD and PD modules, the lens, the optical filter, and other elements are fixed on a metal member, thermal expansion of the metal member depending on a change in the temperature may considerably affect the operation of the bi-directional optical module, for example, a great change in the optical path. A bi-directional optical module having a thermal expansion problem is quite difficult to meet an optical output requirement that a change in the optical output be within ±1 dB operating temperature range, generally −40 to 85° C.
Korean Patent Registration No. 10-0289040 discloses a bi-directional optical communication module using a single optical fiber. In the disclosed bi-directional optical communication module, a bi-directional optical device including a semiconductor laser having a waveguide and a light receiving element is integrated on a single chip and the bi-directional optical device is optically coupled to a single optical fiber. When the optical fiber is optically coupled to the semiconductor laser and the light receiving element, transmission light emitted from the semiconductor laser is optically coupled to a core of the optical fiber and a cross section of the optical fiber is ground to form an acute angle with respect to the optical fiber to allow reception light emitted from the core of the optical fiber to concentrate on a light receiving area of the bi-directional optical device for optical coupling.
One way to prevent an assembling failure of the existing bi-directional optical communication module is to integrate a semiconductor laser and a light receiving element on a single chip, which, however, results in a deterioration of a light focusing power, making it difficult to achieve transceiving of the light.
Korean Patent Publication No. 2003-0032774 discloses a bi-directional optical module having an optical transmitting function through a single optical fiber. The disclosed bi-directional optical module is configured such that a light receiving block, an LD block and a double-sided m-PD block are fixedly installed on equipment in which of a light source, an optical filter and a lens are assembled. The use of the assembling equipment reduces the number of optical components of the bi-directional optical module and the number of processes for performing laser welding. However, it is quite difficult to achieve miniaturization of the bi-directional optical module.